Strategies for Fast Fission Matrix Estimation with Fuel Temperature and Control Rod Feedback

Monte Carlo methods are useful for simulating new reactor designs, but even with advances in computing, these methods still require a significant amount of time to perform transient or multiphysics calculations coupled with thermal modeling.

This work demonstrates a hybrid reactor physics method that uses Monte Carlo to precalculate an initial database of fission matrix parameters, then combines these results for fast calculations on arbitrary system states. This paper extends previous work that demonstrated these methods on the Penn State Breazeale Reactor (PSBR). Approaches for reducing time and memory cost and increasing the accuracy in reproducing Monte Carlo output are considered. For modeling fuel temperature, a representative temperature distribution is used while tallying the initial fission matrix database. Different approaches for modeling the coupling between individual control rod insertions as well as control and fuel temperature effects are presented as well.

Individual solutions are completed in less than 1 s on a single core, and error with respect to Monte Carlo is within 35 pcm for multiplication factor, 0.6% root-mean square, and 2.8% maximum for the normalized three-dimensional fission source distribution on critical, steady-state configurations. Further qualification on different reactor types is needed, but the simplicity and flexibility of this method make further development promising.